1. Field of the Invention
The present invention is directed to a method for the operation of a magnetic resonance apparatus and to a magnetic resonance apparatus for the implementation of the method.
2. Description of the Prior Art
Magnetic resonance technology is a known technique for producing images of the inside of the body of an examination subject. To that end, rapidly switched gradient fields are superimposed on a static basic magnetic field in a magnetic resonance apparatus. For triggering magnetic resonance signals, radio-frequency signals are emitted into the examination subject, and the magnetic resonance signals that are triggered thereby are registered and image datasets and magnetic resonance images are produced on the basis thereof.
In general in the medical field, all methods that use a repeated scanning of a structure of organs and tissues in order to image temporally changing processes such as physiological functions or pathological events are referred to as functional imaging. This term has a narrower meaning in the context magnetic resonance techniques, namely methods that make it possible to identify and image the cerebral sulci in the nervous system, particularly cerebral sulci of a patient, that are stimulated by sensory stimuli and/or by a motor, sensory or cognitive task. Such stimuli can be, for example, acoustic or visual stimuli. In the simplest case, one of the motor tasks can be a defined movement, for example a movement of the hand or a finger.
The BOLD effect (blood oxygen level dependent) is thereby the basis of functional magnetic resonance imaging. The BOLD effect is based on the fact that oxygenated and de-oxygenated hemoglobin in the blood have different magnetic properties. An intensified neural activity in the brain is thereby locally associated with an increased delivery of oxygenated blood, this effecting a corresponding increase in intensity at the location in a magnetic resonance image generated with a gradient echo sequence. The BOLD effect occurs with a time delay of a few seconds following an event that triggers the neural activity.
In functional magnetic resonance imaging, for example, three-dimensional image datasets of the brain are registered every two through four seconds, for example with an echo planar method. Echo planar methods have the advantage that the image dataset registrationxe2x80x94with fewer than 100 ms required for an individual, three-dimensional image datasetxe2x80x94is very fast. Image datasets with or without a specific neural activity are thereby registered at different points in time. For producing a functional image, the image datasets registered with the neural activity are compared for signal differences to those without the neural activity, to identify active brain areas. To ensure that the functional image contains the desired functional information, the respective image datasets registered with the neural activity and the image datasets registered without the neural activity are averaged, for example before the comparison, due to the fact that the BOLD effect is comparatively weak in terms of being able to be registered by magnetic resonance technology. This reduces the probability of correctly determining whether a particular image dataset was registered with or without neural activity, or requires that a number of image datasets be registered in order to arrive at a functional information having the same correctness probability. The latter, among other things, causes an undesired lengthening of the examination time.
An object of the present invention is to provide an improved method for the operation of a magnetic resonance apparatus as well as a magnetic resonance apparatus for the implementation of this method with which, among other things, functional information having a high correctness probability can be acquired in a time-efficient way.
This object is achieved in accordance with the invention in a first embodiment of a method for the operation of a magnetic resonance apparatus wherein a prescribable event that can trigger a neural activity of an examination subject is initiated, the implementation of the event and the readiness of a sensory receptor of the examination subject for the event that triggers the neural activity are monitored, and given a positive result of the monitoring, an image dataset of a region of the examination subject, to which the event can be allocated, is registered.
This object is achieved in a second embodiment of a method for the operation of a magnetic resonance apparatus wherein image datasets of a region of an examination subject to be imaged and to which a prescribable neural activity is to be allocated are registered, whereby the activity can have an event allocated to it that can trigger the activity, an occurrence of the event and the readiness of a sensory receptor of the examination subject for the event triggering the activity are monitored, a result of the monitoring is allocated to the respective image dataset, and image datasets to which a positive result is allocated are further-processed in common.
Compared to a conventional magnetic resonance imaging wherein image datasets for which a clear decision cannot be made as to whether they contain neural activity nevertheless processed for identifying a functional information, the inventive method achieves a higher correctness probability of the functional information given the same number of image datasets, or the functional information can be acquired with the same correctness probability and fewer image datasets, and thus in a more time-efficient way.
By registering and recording the readiness of the subject for reactions to and/or interactions with the event, for example, in the framework of functional magnetic resonance imaging, only those image datasets are further-processed that are unambiguously correlated with the reaction and/or interaction of the patient. As a result, the method can also be particularly utilized in a functional magnetic resonance examination of infirm patients from whom the willingness to cooperate that is required for interaction of the patient cannot always be counted on, or cannot be counted on for the entire duration of the examination.